Near-Eye-Display (NED) systems superimpose computer-generated images (“CG images”) over a user's view of a real-world environment. For example, a NED system may generate composite views to enable a user to visually perceive a CG image superimposed over a physical object that exists within the real-world environment. In some instances, a user's experience is highly dependent on the NED system accurately tracking the user's eye movements. For example, in some instances the NED system may track an interpupillary distance (IPD) of the user. One reason for tracking IPD is so that CG images can be rendered at a suitable separation within the user's field of view. Additionally, or alternatively, the NED system may track a depth at which the user is focusing within the real-world environment. One reason for tracking the user's focal depth (e.g., accommodation plane) is because the user may experience motion sickness or vertigo if CG images are rendered at a depth that is different (i.e., closer to/farther from the user) than that which the user is focusing.
Some conventional eye tracking systems illuminate the user's eyes with near infrared light and then track the user's eye movements by observing reflective patterns that are formed from the near infrared light. For example, upon being illuminated with near infrared light, the eyes may form one or more first Purkinje reflections (e.g., “glints”) that are distributed around the iris. Conventional eye tracking systems track eye movements (e.g., the user's gaze direction) by analyzing the location(s) of these Purkinje reflections with respect to the center of the pupil.
In some instances, convention eye tracking systems estimate the user's line of sight by observing the Purkinje reflections with the addition of head tracking information. Unfortunately, even an accurate estimation of the user's line of sight may be insufficient to accurately determine the depth at which the user is focusing within the real-world environment. This is because the user's line of sight and the user's visual axis (which actually propagates to the user's fovea) only converge at a single depth plane.
It is with respect to these and other considerations that the disclosure made herein is presented.